I've recently had a dramatic (8 mpg) loss in mpg and generally feel the car is struggling where before it didn't. Engine light has gone on and off a few times but I never checked the code, assuming it was probably an air filter or PCV. I since replaced the spark plugs and air filter, and this morning, after having looked at threads here, changed the PCV, cleaned the throttle (with throttle body cleaner) and cleaned the MAF (with MAF cleaner). The struggling problem still exists and now it seems that when I stop, the engine idles higher than usual for a few moments before calming down. Local garage says they can't check the codes before tomorrow. Any thoughts in the meantime why the PCV/MAF/Throttle cleaning might have caused unusually high idling?
First, I'm sure you know how to spell nice person-ume. You really need the codes, and the local mechanic, unless they have the correct Toyota software, may not be able to retrieve them. It's possible to harm the MAF sensor and throttle body with overly aggressive cleaning. On older cars, high idle was one symptom of a vacuum leak IIRC. The PVC valve work may have affected that. How many miles on the engine, and any noticeable oil consumption? Any new noises?
Thanks for the advice. The car has 107K miles on it. I followed the battery test outlined here and got slightly low readings. Unloaded: 11.9 rather than recommended 12.4 minimum Current (power but no brake) load: 11.5v Ready mode: 14v Is that low enough to cause 8 mpg drops? I brought the car to a dealer who found P1121, coolant flow valve, problem. They repaired it free because of the TSB. I'll take another look at the throttle tomorrow, but right now I'm guessing (yes, assuming) that I screwed up and probably moved some crud in a way that is getting in the way. They also found a leaking axle seal and leaking exhaust gasket with deteriorated hardware, which are, I assume, unrelated to the drop in MPG.
Most likely. In ready mode, you're basically reading the output of the charging system. At rest and under load with the car off is how you should test the battery. 11.9 dropping to 11.5 under a slight load is a bad sign for the 12V. Your car's working extra hard trying to charge a battery that's not wanting to be charged. But I think it's still a good idea to check the codes with a reader that can get all the codes from a Prius. Happy hunting.
11.9 volts with the car off is what I got after leaving the driver's door ajar for about 18 hours, not good at all. That's one thing you should deal with right away. If it's not too old (say less than 4 years) I would try a full charging session with a smart charger, 4 amp range, see how it goes. If older just replace it. That may be just one of your problems, but worth dealing with asap.
I agree the 12V is bad. 11.8 at rest is essentially discharged. But I don't think it'll noticeably bog down your acceleration and cause that much of a drop in mileage. I read somewhere the effect might be as high as 2 mpg, but that wasn't an unimpeachable source, just a guy on the internet. Did you spray the throttle body liberally with the TB cleaner? Did you remove the MAF for cleaning?
I cleaned the throttle body by spraying a towel and wiping around. To go further down I sometimes wrapped the towel around a screwdriver and gently wiped the sides. In the past I've seen people say not to spray inside the throttle body, probably similar to your "guy on the internet" though, so I'm happy to be better educated. I did remove the MAF for cleaning. I sprayed the bulbous thingy, sprayed inside the MAF, let it sit to dry for a few minutes and then replaced it.
Did you also clean and lubricate the throttle butterfly axle and spring while you had the MAF out? Does it move freely? It may very well be related, depending on where the exhaust gasket that you are talking about is. I wouldn't worry about the 12 V battery for the moment, that is the least of your worries. Charge it up overnight and then re-test to see if the resting voltage and the voltage under load come up. If not replace that sucker and be done with it. But, like I said, the 12 V battery is just a side issue. Just to add my +1 to getting the codes, otherwise you will continue to nice person-ume.
Thank you everybody for the help. I recleaned the throttle body and MAF this morning, but haven't had a chance to go for a drive yet - we've got an ice storm locally with gobs of accidents everywhere. Allowed to idle, the idle seems high for a few moments before lowering rpm. If it doesn't correct itself soon then I'll try tightening the PCV a bit, or clean again (and again). Nobody local has the Optima everyone here recommends, so I ordered the DS46B24R from Amazon to replace the one I installed five or so years ago. I'll update when I've got more information. Somewhere else here I saw it stated that replacing the entire exhaust, rather than welding pieces of the exhaust, is more sensible. I'll likely go that route once the weather warms. But if any of you experts want to tell me to do anything different, with anything I've got planned, please do chime in as I appreciate the advice.
Anytime you clean the throttle body and MAF sensor it's a very good idea to disconnect the 12 Volt battery for a few minutes to reset all of the computers. Over time the ECM will make fuel/air trim adjustments to compensate for the MAF and TB as they get dirty. If you clean them without a reset the engine will run rich and it won't idle right. Cleaning the MAF and TB is something we do on every Prius that we work on, no matter what the job is. I've seen cars that wouldn't idle correctly as well as cars that wouldn't run at all (post cleaning) and it's normally proportional to how dirty the intake was before the cleaning. Actually anytime you do anything to a Prius you should disconnect the 12 volt to reset everything. Make sure that the car is on level ground when you reconnect the battery or else your fuel gauge will be off. Matt
I did exactly that yesterday morning - left the negative off for ten minutes. Idling seemed to be back to normal, did some driving and mpg was back up. Still, as per earlier suggestions, I'll replace the 12v. Again, thank you to everybody for your expert advice. Greatly appreciated.
Maybe. But it is definitely low enough to indicate that it's time for a new battery. Likely that other odd things will start happening too. Make sure you charge the new one BEFORE installing it. Then check the charging voltage after installing.....in READY mode (running).
You ever fix this?? I wish people would remember to post the solution. So much troubleshooting on this forum and so few came back to say what fixed their problem.
